Glad you had some fun. I'll be around Monday, if you want, for some Rook training! There are some great guides around the forums, but here are some quick tips for beginners:
1. Health stack! You need all the +HP items you can get. Nimoth's, Blood of the Fallen, and Unbreakable boots are great for starters.
2. You're slow, and thus easily killed(gankable). On Cataract, don't tread much past the halfway point unless you have a friend with you, or you have some speed items.
3. If your hammer slam isn't going to hit, right click someplace else to cancel it and save the mana.